An easy lock repair
A common problem on pipe key locks is the drill pin coming loose, or being lost completely. As well as some safe locks (many, but not exclusively, old) there are millions of old cabinet locks, which can be made reliable with a simple repair. If the drill pin is missing or loose, the key operation is at best unreliable.
Locks are less commonly fitted and used on furniture today. However, they remain useful for privacy, especially in households with children or grandchildren. Replacement of faulty locks could sometimes be cheaper, but not all locksmiths carry a wide range of cabinet locks. Victorian and Edwardian furniture had locks in a range of sizes, not all of which are obtainable today. Older warded locks are even more difficult to replace, but millions are still in service.
Re-rivetting the drill pin, or fitting a new one, is the proper solution. In an old Willen catalogue, drill pins were offered in sizes 6g – 12g @ 4/6 per gross, so old locksmiths/ironmongers must have done many such repairs.
Another possible solution for some cabinet locks is to drill a hole in the backplate of the same gauge as the keyhole. This converts the lock to use a pin key, but is not suitable if the lock is one of a suite keyed alike — such as much cabinet furniture.
The tools needed are a ball peen (also spelled, pein) hammer with a hard flat face — a 4oz one is sufficient, as riveting locks is light work. There are several other types of peening hammer, and heavier ones, mainly used in blacksmithing. Small drill bits and needle files are also useful. A small vice or anvil of some sort (e.g. the back of a vice), and an electric drill with horizontal drill stand — or a lathe — is needed. Occasionally, a small grinding wheel can be handy — in a Dremel-type tool, for example.
Keeping the drill pin square to the lock backplate is very important — the pin is what guides the key’s revolution, rather than the keyhole in the lockcase, which might even be oversize without impairing the lock. For a small cabinet lock it usually is sufficient simply to grip the pin in a small vice, and hammer the other end of the pin. Or even just resting the end of the pin on a small anvil. This is, in effect, the same as forming the head on a rivet, using taps from a small ball peen hammer, striking glancing blows outwards from the middle of the protruding end of the pin.
Existing pin present but loose.
Rest the tip of the pin on an anvil, or grip the pin in a small vice. Using the ball end of the hammerhead, strike light glancing blow outwards from the centre of the pin, working around a circle. When peening a rivet, one must resist the natural temptation to treat it like a nail. The idea is not to simply hammer away at the face of the rivet end, smashing it into oblivion. Peening a rivet head is actually a careful metal forming operation. It is actually rolling an edge on a small metal rod.
Be aware that it does not take great force to peen a rivet. Work slowly at it, it will not be a long job once started. Most cabinet locks had the pins filed and polished flush with the backplate. If there is enough metal, a stronger fixing is made by leaving the bucktail domed — see below on new pins.
Two other techniques are available if the hole is worn oversize. Hitting the centre of the drill pin tail dead centre a smart blow with a centre punch can expand the pin enough to tighten it in its hole. Alternatively, setting the centre punch at 45° and punching lightly all around the hole can shrink the hole enough to grip the pin tightly.
The final two expedients are more bother. A drill pin can be soldered in place. Using hard solder (i.e. silver solder, or brazing) is best, but involves making the pin and backplate very hot. Even with a tiny pencil flame, that can be risky on small brass locks. Soft solder is safer, and better than nothing.
Heat the end of the silver solder rod and dip it in the flux powder, the powder will stick to the rod, (there is no need to make a paste). Make the joint cherry red then touch rod on the junction of backplate and pin, then the solder will run into the joint.
The metal of the joint should be hot enough to melt the solder. If it is not the solder will just form small beads and drop off because your flame (or soldering iron for soft solder) will simply melt the rod. Keep the flame away from the solder rod. For soft solder, an active flux is preferable to resin (or resin-cored solder). All flux residue must afterwards be washed away, or it will promote corrosion.
Lastly, a new drill pin can be formed with a collar on the inside of the lockplate.
New Pin needed?
The commercially available ones have a shoulder formed on them. Today, it is fairly easy to make one with a round wire nail, if the hole in the lock plate is not too large. If no suitable pin is to hand, one can be made by cutting a wire nail to length (actually, a little over-long at this stage, it can be shortened later), then forming a neck on one end, by reducing the diameter of the buck-tail for a length equal to about twice the thickness of the lockcase backplate. A lathe is the ideal tool, but not really needed. Chuck a nail in an electric drill (preferably in a horizontal stand), and form a shoulder by lightly resting a fine flat file on the nail. If the small diameter buck-tail is made too long, no problem, it can later be filed/ground shorter.
The bucktail is next bluntly pointed, by hitting it on four sides with the flat of the hammerhead.
Insert the small end of the pin, the buck-tail, through the clearance hole in the lockcase. With the pin shaped to almost a point, lightly hit it straight down from the top with the flat head, to flatten it outwards, then, hitting it glancing blows on a diagonal, work around in circles. This should cause the head of the pin to begin to mushroom out. Thus the tail is upset, or bucked (i.e. deformed), by peening the protruding tail so that it expands to about 1½ times the original shaft diameter, with the ball peen hammer head. The head will take many rapid hammer blows working in an increasing circular motion towards the outside. The slightly domed edge of the tail should not split, and the dimples in it should be small enough to need a magnifying glass to see them.
It might be possible to grip the pin in a vice, with the lockcase resting on the vice jaws, to keep the pin upright. If this is not possible, the end of the pin is simply rested on something sturdy to act as an anvil. Riveting with solid rivets (which effectively is what this process is) is less used these days than in the past, but it is a basic, and very old, metalworking technique, and still has its uses.
If the hole in the lock plate is already worn over-size, it will be necessary to start with a bigger nail. Form the buck-tail as before, then file down the pin for the key to fit on it, almost to the backplate. Leave a small upstanding collar, about 2-3mm thick and perhaps twice the diameter of the pin, so the drill pin is firmly and strongly rivetted in place. But now the key will not enter the lock quite fully. Then file off the very end of the key pipe until the key fully enters the lock and turns smoothly. The collar inside the lock thus acts as an additional ward, and the repair now ADDS to the lock’s security. The key thus altered will still fit any other existing locks keyed-alike with it.
Lastly, trim the drill pin to suitable length, and slightly round the end to ease inserting the key. Lever gates on most small cabinet locks are wide enough to be tolerant of slight inaccuracy in how upright the drill pin is, but the lock’s function should finally be tested.
Have a try for practice on a scrap of sheet metal or old lock first, it is not difficult.
Incidentally, the drill pins of old locks were practically wards, with three different gauges and lengths sometimes used. The pipe keys were drilled to matching depths. The thinnest gauge pin was the longest, standing well above the lockcase and more sharply pointed. The middle thickness was flush with the outside surface of the lockcase and slightly rounded. The thickest one was below the level of the lockcase, and flat-topped, as the keyhole guided the key into the lock. These pins almost fill the keyhole. This practice is now uncommon.
Anyone who is competent at re-fixing drill pins is likely to find his services useful to antique dealers and furniture restorers. This is a job which often can be done when the shop is otherwise quiet, with no customers.
Richard Phillips began collecting locks as a teenager in the early 1960s. He was involved in crime prevention for three decades.